Vietnamese authorities have seized 619 kilograms (1,362 pounds) of ivory smuggled from Africa after finding 4 tons at the same port over the past two months, state media and an official said Friday. The ivory seized Thursday had been hidden in two containers arriving at Cat Lai port in southern commercial hub of Ho Chi Minh City, the Customs newspaper said.

Le Dinh Loi, the city’s deputy customs chief confirmed the report, but did not give more details Friday. The smugglers used more sophisticated tactics than previous shipments by packing wax around the ivory when it was sealed inside emptied-out timber and using wood nails to evade X-ray checks, according to the newspaper, published by the General Department of Customs.

The seizure came just a week after leaders and senior officials from more than 40 countries met at an international conference on illegal wildlife trade in Hanoi, which was attended by Britain’s Prince William. The conference called for stepped-up efforts to combat illegal wildlife trade.

At the conference, Prince William, who is president of United for Wildlife, praised Vietnam, China and other Asian countries for taking steps to battle wildlife trafficking, but said rhinos, elephants, pangolins and tigers are still being killed in horrifying numbers. He said the international community is not moving fast enough to keep up with the crisis.

Vietnam is one of the world’s major transit points and consumers of ivory and rhino horn. Elephant ivory is used as jewelry and home decorations in Vietnam, which bans hunting of its own dwindling population of elephants.